Silicon-germanium based optical filter

ABSTRACT

An optical filter may include a substrate. An optical filter may include a set of optical filter layers disposed onto the substrate. The set of optical filter layers including a first subset of optical filter layers. The first subset of optical filter layers may include a silicon-germanium (SiGe) with a first refractive index. An optical filter may include a second subset of optical filter layers. The second subset of optical filter layers may include a material with a second refractive index. The second refractive index being less than the first refractive index.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/228,184, filed Dec. 20, 2018 (now U.S. Pat. No. 11,041,982), which isa continuation of U.S. patent application Ser. No. 15/365,540, filedNov. 30, 2016 (now U.S. Pat. No. 10,168,459), the contents of which areincorporated herein by reference in their entireties.

BACKGROUND

An optical transmitter may emit light that is directed toward an object.For example, in a gesture recognition system, the optical transmittermay transmit near infrared (NIR) light toward a user, and the NIR lightmay be reflected off the user toward an optical receiver. In this case,the optical receiver may capture information regarding the NIR light,and the information may be used to identify a gesture being performed bythe user. For example, a device may use the information to generate athree dimensional representation of the user, and to identify thegesture being performed by the user based on the three dimensionalrepresentation.

In another example, information regarding the NIR light may be used torecognize an identity of the user, a characteristic of the user (e.g., aheight or a weight), a characteristic of another type of target (e.g., adistance to an object, a size of the object, or a shape of the object),or the like. However, during transmission of the NIR light toward theuser and/or during reflection from the user toward the optical receiver,ambient light may interfere with the NIR light. Thus, the opticalreceiver may be optically coupled to an optical filter, such as abandpass filter, to filter ambient light and to allow MR light to passthrough toward the optical receiver.

SUMMARY

According to some implementations, an optical filter may include asubstrate. An optical filter may include a set of optical filter layersdisposed onto the substrate. The set of optical filter layers includinga first subset of optical filter layers. The first subset of opticalfilter layers may include a silicon-germanium (SiGe) with a firstrefractive index. An optical filter may include a second subset ofoptical filter layers. The second subset of optical filter layers mayinclude a material with a second refractive index. The second refractiveindex being less than the first refractive index.

According to some implementations, an optical filter may include asubstrate. An optical filter may include a high refractive indexmaterial layer and a low refractive index material layer disposed ontothe substrate to filter incident light. Wherein a first portion of theincident light with a first spectral range is to be reflected by theoptical filter and a second portion of the incident light with a secondspectral range is to be passed through by the optical filter. The highrefractive index material layers being hydrogenated silicon-germanium(SiGe:H). The low refractive index material layers being silicon dioxide(SiO₂).

According to some implementations, an optical system may include anoptical transmitter to emit near-infrared (NIR) light. An optical systemmay include an optical filter to filter an input optical signal andprovide the filtered input optical signal. The input optical signalincluding the NIR light from the optical transmitter and ambient lightfrom an optical source. The optical filter including a set of dielectricthin film layers. The set of dielectric thin film layers including afirst subset of layers of silicon-germanium with a first refractiveindex. A second subset of layers of a material with a second refractiveindex less than the first refractive index, the filtered input opticalsignal including a reduced intensity of ambient light relative to theinput optical signal. An optical system may include an optical receiverto receive the filtered input optical signal and provide an outputelectrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are diagrams of an overview of an example implementationdescribed herein;

FIGS. 2A and 2B are diagrams of an example of optical characteristicsfor a set of materials relating to an example implementation describedherein;

FIG. 3A is a diagram of an example of mechanical characteristics for aset of materials relating to an implementation described herein;

FIG. 3B is a diagram of another example of optical characteristics for aset of materials relating to an example implementation described herein;

FIG. 4 is a diagram of an example implementation described herein;

FIGS. 5A and 5B are diagrams of another example of opticalcharacteristics for a set of materials relating to an exampleimplementation described herein;

FIG. 5C is a diagram of another example of mechanical characteristicsfor a set of materials relating to an example implementation describedherein; and

FIGS. 6A and 6B are diagrams of another example implementation describedherein.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

An optical receiver may receive light from an optical source, such as anoptical transmitter. For example, the optical receiver may receive nearinfrared (NIR) light from the optical transmitter and reflected off atarget, such as a user or an object. In this case, the optical receivermay receive the NIR light as well as ambient light, such as visiblespectrum light. The ambient light may include light from one or morelight sources separate from the optical transmitter, such as sunlight,light from a light bulb, or the like. The ambient light may reduce anaccuracy of a determination relating to the NIR light. For example, in agesture recognition system, the ambient light may reduce an accuracy ofgeneration of a three-dimensional image of the target based on the NIRlight. Thus, the optical receiver may be optically coupled to an opticalfilter, such as a bandpass filter, to filter ambient light and to passthrough NIR light toward the optical receiver.

The optical filter may include a set of dielectric thin film layers. Theset of dielectric thin film layers are selected and deposited to block aportion of out-of-band light below a particular threshold, such as 700nanometers (nm), and pass light for a particular range of wavelengths,such as a range of approximately 700 nm to approximately 1700 nm, arange of approximately 800 nm to approximately 1100 nm, a range ofapproximately 900 nm to approximately 1000 nm, a range of approximately920 nm to approximately 980 nm, or the like. For example, the set ofdielectric thin film layers may be selected to filter out the ambientlight. Additionally, or alternatively, the set of dielectric film layersmay be selected to block out-of-band light below the particularthreshold, and to pass light for another range of wavelengths, such as arange of approximately 1500 nm to approximately 1600 nm, a range ofapproximately 1520 nm to approximately 1580 nm, or at a wavelength ofapproximately 1550 nm.

Implementations, described, herein, may utilize a silicon-germanium(SiGe) based material, such as hydrogenated silicon-germanium (SiGe:H)material or the like, as a set of high index layers for an opticalfilter, such as low angle shift optical filter. In this way, based onhaving a higher effective refractive index relative to another filterstack that uses another high index layer material, the optical filtermay provide a relatively low angle-shift. Moreover, a filter using theSiGe or SiGe:H material may substantially block or effectively screenout ambient light and pass through NIR light. The wavelength shift at aparticular angle of incidence may be calculated as:

${{\lambda_{shift}(\Theta)} = {\lambda_{0}\left( {1 - \frac{\sqrt{n_{eff}^{2} - \left( {\sin\;\Theta} \right)^{2}}}{n_{eff}}} \right)}};$

where λ_(shift) represents a wavelength shift at a particular angle ofincidence, Θ represents the particular angle of incidence, n_(eff)represents the effective refractive index, and λ₀ represents thewavelength of light at Θ=0°.

FIGS. 1A-1D are diagram of an example 100 of a set of geometries forsputter deposition systems for manufacturing example implementationsdescribed herein.

As shown in FIG. 1, example 100 includes a vacuum chamber 110, asubstrate 120, a cathode 130, a target 131, a cathode power supply 140,an anode 150, a plasma activation source (PAS) 160, and a PAS powersupply 170. Target 131 may include a silicon-germanium material in aparticular concentration selected based on optical characteristics ofthe particular concentration, as described herein. In another example,an angle of cathode 130 may be configured to cause a particularconcentration of silicon-germanium to be sputtered onto substrate 120,as described herein. PAS power supply may be utilized to power PAS 160and may include a radio frequency (RF) power supply. Cathode powersupply 140 may be utilized to power cathode 130 and may include a pulseddirect current (DC) power supply.

With regard to FIG. 1A, target 131 is sputtered in the presence ofhydrogen (H₂), as well as an inert gas, such as argon, to deposit ahydrogenated silicon-germanium material as a layer on substrate 120. Theinert gas may be provided into the chamber via anode 150 and/or PAS 160.Hydrogen is introduced into the vacuum chamber 110 through PAS 160,which serves to activate the hydrogen. Additionally, or alternatively,cathode 130 (e.g., in this case, hydrogen may be introduced from anotherpart vacuum chamber 110) or anode 150 may cause hydrogen activation(e.g., in this case, hydrogen may be introduced into vacuum chamber 110by anode 150). In some implementations, the hydrogen may take the formof hydrogen gas, a mixture of hydrogen gas and a noble gas (e.g., argongas), or the like. PAS 160 may be located within a threshold proximityof cathode 130, allowing plasma from PAS 160 and plasma from cathode 130to overlap. The use of the PAS 160 allows the hydrogenated silicon layerto be deposited at a relatively high deposition rate. In someimplementations, the hydrogenated silicon-germanium layer is depositedat a deposition rate of approximately 0.05 nm/s to approximately 2.0nm/s, at a deposition rate of approximately 0.5 nm/s to approximately1.2 nm/s, at a deposition rate of approximately 0.8 nm/s, or the like.

Although the sputtering procedure is described, herein, in terms of aparticular geometry and a particular implementation, other geometriesand other implementations are possible. For example, hydrogen may beinjected from another direction, from a gas manifold in a thresholdproximity to cathode 130, or the like.

As shown in FIGS. 1B-1C, a similar sputter deposition system includes avacuum chamber 110, a substrate 120, a first cathode 180, a secondcathode 190, a silicon target 181, a germanium target 191, a cathodepower supply 140, an anode 150, a plasma activation source (PAS) 160,and a PAS power supply 170. In this case, silicon target 181 is asilicon target and germanium target 191 is a germanium target.

As shown in FIG. 1B, silicon target 181 is oriented at approximately 0degrees relative to substrate 120 (e.g., approximately parallel tosubstrate 120) and germanium target 191 is oriented at approximately 120degrees relative to substrate 120. In this case, silicon and germaniumare sputtered by cathode 180 and cathode 190, respectively from silicontarget 181 and germanium target 191, respectively, onto substrate 120.

As shown in FIG. 1C, in a similar sputter deposition system, silicontarget 181 and germanium target 191 are each oriented at approximately60 degrees relative to substrate 120, and silicon and germanium aresputtered by cathode 180 and cathode 190, respectively, from firsttarget 181 and second target 191, respectively, onto substrate 120.

As shown in FIG. 1D, in a similar sputter deposition system, silicontarget 181 is oriented at approximately 120 degrees relative tosubstrate 120 and germanium target 191 is oriented at approximately 0degrees relative to substrate 120. In this case, silicon and germaniumare sputtered by cathode 180 and cathode 190, respectively from silicontarget 181 and germanium target 191, respectively, onto substrate 120.

With regard to FIGS. 1A-1D, each configuration of components in asilicon sputter deposition system may result in a different relativeconcentration of silicon and germanium. Although, described, herein, interms of different configurations of components, different relativeconcentrations of silicon and germanium may also be achieved usingdifferent materials, different manufacturing processes, or the like.

As indicated above, FIGS. 1A-1D are provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIGS. 1A-1D.

FIGS. 2A and 2B are diagrams of an example of characteristics relatingto using an example implementation described herein.

As shown in FIG. 2A, and by chart 210, a set of characteristics aredetermined, for example, for a SiGe layer (e.g., a SiGe:H layer for usein an optical filter). Assume that an increase in cathode angle of acathode sputtering silicon corresponds to an increased germanium contentin the optical filter relative to a silicon content, as described infurther detail with regard to FIGS. 1B-1D. For example, for high indexlayers of an optical filter, deposited at 30 degrees, the high indexlayer may be associated with an approximately 7.5% germanium content.Similarly, for deposition at 35 degrees the optical filter may beassociated with an approximately 22% germanium content, and fordeposition at 50 degrees the optical filter may be associated with anapproximately 90% germanium content.

As further shown in FIG. 2A, and by chart 210, a refractive index n at awavelength of 950 nm is provided for a set of layers based on a cathodeangle (in degrees) at which sputtering was performed to sputter materialto form the set of high index material single layers. As shown, for asilicon-germanium (SiGe) and annealed silicon-germanium (SiGe-280C)(e.g., silicon-germanium for which an annealing procedure has beenperformed at 280 degrees Celsius (C)) based high index single layer orSiGe single layers, an increase in cathode angle corresponds to anincrease in refractive index. Moreover, the refractive index for siliconlayers including germanium is greater than for silicon not includinggermanium, such as a silicon (Si) based optical filter and an annealedsilicon (Si-280C) based optical filter, thereby improving performance ofan optical filter that includes SiGe layers.

As shown in FIG. 2B, and by chart 220, another set of opticalcharacteristics are determined for the SiGe single layers. As shown, anabsorption at a wavelength of 950 nm of the set of SiGe single layers isdetermined in relation to a type of material for the high index layersand a cathode angle used for a sputtering procedure to deposit the highindex layers. For example, increased germanium content (e.g., increasedcathode angle) is associated with increased absorption loss in the SiGelayer. However, annealed silicon-germanium is associated with a reducedabsorption loss for an optical filter associated with a similar cathodeangle relative to non-annealed silicon-germanium. For example, annealedsilicon-germanium may be associated with a loss value that satisfies anabsorption threshold for utilization in optical filters at a cathodeangle that corresponds to a refractive index that satisfies a refractiveindex threshold for utilization in low angle shift for an opticalfilter. In this way, annealing silicon-germanium (or hydrogenatedsilicon-germanium) may permit silicon-germanium (or hydrogenatedsilicon-germanium) to be used as a low-angle shift coating with arelatively high refractive index and without an excessive absorption ofNIR light.

As indicated above, FIGS. 2A and 2B are provided merely as examples.Other examples are possible and may differ from what was described withregard to FIGS. 2A and 2B.

FIGS. 3A and 3B are diagrams of another example of characteristicsrelating to using an example implementation described herein.

As shown in FIG. 3A, and by chart 310, a set of mechanicalcharacteristics are determined for the set of SiGe single layers. Asshown, a stress value (in megapascals (MPa)) of the set of SiGe singlelayers is determined in relation to a type of material for the highindex layers and a cathode angle used for a sputtering procedure todeposit the high index layers. The stress value may be a compressivestress on the SiGe single layer as a result of the sputtering procedure.For example, increased germanium content (e.g., increased cathode angle)is associated with decreased stress for a SiGe single layer. As shown,annealed silicon-germanium is associated with a reduced stress value fora SiGe single layer associated with a similar cathode angle tonon-annealed silicon-germanium. For example, annealed silicon-germaniummay be associated with a stress value that satisfies a stress thresholdfor utilization in optical filters at a cathode angle that correspondsto a refractive index that satisfies a refractive index threshold forutilization in optical filters. Reduced stress value may reduce adifficulty in manufacture when the manufacturing procedure includescutting a wafer into multiple portions for multiple optical filters.Moreover, a reduced stress value may permit a reduced thicknesssubstrate relative to another type of material with a greater stressvalue. In this way, annealing silicon-germanium (or hydrogenatedsilicon-germanium) may permit silicon-germanium (or hydrogenatedsilicon-germanium) to be used as a low-angle shift coating with arelatively high refractive index and without an excessive stress value,thereby improving manufacturability of an optical filter and reducing athickness of the optical filter relative to a non-annealed opticalfilter and especially if compared of filters just using silicon orhydrogenated silicon.

As shown in FIG. 3B, and by chart 320, a set of optical characteristicsare determined for a set of bandpass filters center at 950 nm. As shown,a transmissivity percentage of a first optical filter and a secondoptical filter is determined in relation to a utilization of annealingand a wavelength of light. Assume that a first optical filter,corresponding to reference number 322, and a second optical filter,corresponding to reference number 324, are each associated with a set of4 cavities, a 3.1 micrometer thickness, a silicon-germanium set of highindex layers, a silicon dioxide set of low index layers, noanti-reflective coating on the second side, and a cathode angle of 47.5degrees (e.g., which may correspond to approximately 80% germanium forthe set of high index layers).

With regard to FIG. 3B, and reference numbers 322 and 324, utilizationof annealing improves transmissivity at approximately 950 nm byapproximately 7% (e.g., to greater than 80% or approximately 85% atapproximately 950 nm) relative to not utilizing annealing of an opticalfilter. In this way, annealing silicon-germanium (or hydrogenatedsilicon-germanium) may permit silicon-germanium (or hydrogenatedsilicon-germanium) to be used as a low-angle shift coating with improvedtransmissivity relative to a non-annealed optical filter. In anotherexample, including an anti-reflective coating (e.g., on a backsidesurfacce of the optical filter) may improve transmissivity by anadditional approximately 5% relative to the first optical filter withoutan anti-reflective coating.

Although FIG. 3B shows an example relating to a particular set ofcharacteristics of the first optical filter and the second opticalfilter, other examples described herein may exhibit similarly improvedperformance with annealing for other characteristics of an opticalfilter.

Although FIG. 3B shows an example relating to optical characteristics ofa bandpass filter, similarly improved optical characteristics may beassociated with manufacture of a shortwave pass filter, a long wave passfilter, an anti-reflective coating, a non-polarizing beam splitter, apolarizing beam splitter, a dielectric reflector, a multi-bandpassfilter, a notch filter, a multi-notch filter, a neutral density filter,or the like.

As indicated above, FIGS. 3A and 3B are provided merely as examples.Other examples are possible and may differ from what was described withregard to FIGS. 3A and 3B.

FIG. 4 is a diagram of an example optical filter 400. FIG. 4 shows anexample stackup of an optical filter using a silicon-germanium basedmaterial as a high index material. As further shown in FIG. 4, opticalfilter 400 includes an optical filter coating portion 410 and asubstrate 420.

Optical filter coating portion 410 includes a set of optical filterlayers. For example, optical filter coating portion 410 includes a firstset of layers 430-1 through 430-N+1 (N≥1) and a second set of layers440-1 through 440-N. Layers 430 may include a set of layers of a highrefractive index material (H layers), such as silicon-germanium,hydrogenated silicon-germanium layers, or the like. The SiGe layers mayinclude (small quantities of) phosphorous, boron, nitride, or the like.Layers 440 may include a set of layers of a low refractive indexmaterial (L layers), such as silicon dioxide layers or the like.Additionally, or alternatively, the L layers may include silicon nitridelayers, Ta2O5 layers, Nb2O5 layers, TiO2 layers, Al2O3 layers, ZrO2layers, Y2O3 layers, Si3N4 layers, a combination thereof, or the like.

In some implementations, layers 430 and 440 may be stacked in aparticular order, such as an (H-L)_(m) (m≥1) order, an (H-L)_(m)-Horder, an L-(H-L)_(m) order, or the like. For example, as shown, layers430 and 440 are positioned in an (H-L)_(n)-H order with an H layerdisposed at a surface of optical filter 400 and an H layer disposed at asurface of substrate 420. In some implementations, optical filtercoating portion 410 may be associated with a particular quantity oflayers, m. For example, a hydrogenated silicon-germanium based opticalfilter may include a quantity of alternating H layers and L layers, suchas a range of 2 layers to 200 layers.

In some implementations, each layer of optical filter coating portion410 may be associated with a particular thickness. For example, layers430 and 440 may each be associated with a thickness of between 1 nm and1500 nm, 3 nm and 1000 nm, 600 nm and 1000 nm, or 10 nm and 500 nm,and/or optical filter coating portion 410 may be associated with athickness of between 0.1 μm and 100 μm, 0.25 μm and 100 μm, or the like.In some examples, at least one of layers 430 and 440 may each beassociated with a thickness of less than 1000 nm, less than 600 nm, lessthan 100 nm, or less than 5 nm, and/or optical filter coating portion410 may be associated with a thickness of less than 100 μm, less than 50μm, and/or less than 10 μm. In some implementations, layers 430 and 440may be associated with multiple thicknesses, such as a first thicknessfor layers 430 and a second thickness for layers 440, a first thicknessfor a first subset of layers 430 and a second thickness for a secondsubset of layers 430, a first thickness for a first subset of layers 440and a second thickness for a second subset of layers 440, or the like.In this case, a layer thickness and/or a quantity of layers may beselected based on an intended set of optical characteristics, such as anintended passband, an intended reflectance, or the like.

In some implementations, a particular silicon-germanium based materialmay be selected for the layers 430. For example, layers 430 may beselected and/or manufactured (e.g., via a sputtering procedure) toinclude a particular type of silicon-germanium, such as SiGe-50,SiGe-40, SiGe-60, or the like. In some implementations, layers 430 mayinclude trace amounts of another material, such as argon, as a result ofa sputter deposition procedure, as described herein. In another example,the particular silicon-germanium based material may be manufacturedusing a hydrogenating procedure to hydrogenate the silicon-germaniumbased material, a nitrogenating procedure to nitrogenate thesilicon-germanium based material, one or more annealing procedures toanneal the silicon-germanium based material, another type of procedure,a doping procedure (e.g., phosphorous based doping, nitrogen baseddoping, boron based doping, or the like) to dope the silicon-germaniumbased material, or a combination of multiple procedures (e.g., acombination of hydrogenation, nitrogenation, annealing, and/or doping),as described herein. For example, layers 430 may be selected to includea refractive index greater than that of layers 440 over, for example, aspectral range of approximately 800 nm to approximately 1100 nm, aspectral range of approximately 900 nm to approximately 1000 nm, aparticular wavelength of approximately 950 nm, or the like. In anotherexample, layers 430 may be selected to include a refractive indexgreater than that of layers 440 over, for example, a spectral range ofapproximately 1400 nm to approximately 1700 nm, a spectral range ofapproximately 1500 nm to approximately 1600 nm, a particular wavelengthof approximately 1550 nm, or the like. In this case, layers 430 may beassociated with a refractive index greater than 3, a refractive indexgreater than 3.5, a refractive index greater than 3.8, or a refractiveindex greater than 4. For example, layers 430 may be associated with arefractive index greater than 4 at approximately 954 nm.

In some implementations, a particular material may be selected forlayers 440. For example, layers 440 may include a set of silicon dioxide(SiO₂) layers, a set of aluminum oxide (Al₂O₃) layers, a set of titaniumdioxide (TiO₂) layers, a set of niobium pentoxide (Nb₂O₅) layers, a setof tantalum pentoxide (Ta₂O₅) layers, a set of magnesium fluoride (MgF₂)layers, a set of silicon nitride (S₃N₄) layers, zirconium oxide (ZrOz₂),yttrium oxide (Y₂O₃), or the like. In this case, layers 440 may beselected to include a refractive index lower than that of the layers 430over, for example, a spectral range of approximately 800 nm toapproximately 1100 nm, the spectral range of approximately 900 nm toapproximately 1000 nm, the wavelength of approximately 954 nm, or thelike. For example, layers 440 may be selected to be associated with arefractive index of less than 3 over the spectral range of approximately800 nm to approximately 1100 nm. In another example, layers 440 may beselected to be associated with a refractive index of less than 2.5 overthe spectral range of approximately 800 nm to approximately 1100 nm, thespectral range of approximately 900 nm to approximately1000 nm, thewavelength of approximately 954 nm, or the like. In another example,layers 440 may be selected to be associated with a refractive index ofless than 2 over the spectral range of approximately 800 nm toapproximately 1100 nm, the spectral range of approximately 900 nm toapproximately 1000 nm, the wavelength of approximately 954 nm, or thelike. In some implementations, layers 430 and/or 440 may be associatedwith a particular extinction coefficient, such as an extinctioncoefficient of below approximately 0.007, an extinction coefficient ofbelow approximately 0.003, an extinction coefficient of belowapproximately 0.001, or the like over a particular spectral ranges(e.g., the spectral range of approximately 800 nm to approximately 1100nm, the spectral range of approximately 900 nm to approximately 1000 nm,the wavelength of approximately 954 nm, or the like; and/or a spectralrange of approximately 1400 nm to approximately 1700 nm, a spectralrange of approximately 1500 nm to approximately 1600 nm, a particularwavelength of approximately 1550 nm, or the like). In someimplementations, the particular material may be selected for layers 440based on a desired width of an out-of-band blocking spectral range, adesired center-wavelength shift associated with a change of angle ofincidence (AOI), or the like.

In some implementations, optical filter coating portion 410 may befabricated using a sputtering procedure. For example, optical filtercoating portion 410 may be fabricated using a pulsed-magnetron basedsputtering procedure to sputter alternating layers 430 and 440 on aglass substrate or another type of substrate. In some implementations,multiple cathodes may be used for the sputtering procedure, such as afirst cathode to sputter silicon and a second cathode to sputtergermanium. In this case, the multiple cathodes may be associated with anangle of tilt of the first cathode relative to the second cathodeselected to ensure a particular concentration of germanium relative tosilicon. In some implementations, hydrogen flow may be added during thesputtering procedure to hydrogenate the silicon-germanium. Similarly,nitrogen flow may be added during the sputtering procedure tonitrogenate the silicon-germanium. In some implementations, opticalfilter coating portion 410 may be annealed using one or more annealingprocedures, such as a first annealing procedure at a temperature ofapproximately 280 degrees Celsius or between approximately 200 degreesCelsius and approximately 400 degrees Celsius, a second annealingprocedure at a temperature of approximately 320 degrees Celsius orbetween approximately 250 degrees Celsius and approximately 350 degreesCelsius, or the like. In some implementations, optical filter coatingportion 410 may be fabricated using a SiGe:H coated from a target, asdescribed with regard to FIGS. 1A-1D. For example, a SiGe compoundtarget with a selected ratio of silicon to germanium may be sputtered tofabricate optical filter coating portion 410 with a particular siliconto germanium ratio.

In some implementations, optical filter coating portion 410 may beassociated with causing a reduced angle shift relative to an angle shiftcaused by another type of optical filter. For example, based on arefractive index of the H layers relative to a refractive index of the Llayers, optical filter coating portion 410 may cause a reduced angleshift relative to another type of optical filter with another type ofhigh index material.

In some implementations, optical filter coating portion 410 is attachedto a substrate, such as substrate 420. For example, optical filtercoating portion 410 may be attached to a glass substrate or another typeof substrate. Additionally, or alternatively, optical filter coatingportion 410 may be coated directly onto a detector or onto a set ofsilicon wafers including an array of detectors (e.g., usingphoto-lithography, a lift-off process, etc.). In some implementations,optical filter coating portion 410 may be associated with an incidentmedium. For example, optical filter coating portion 410 may beassociated with an air medium or a glass medium as an incident medium.In some implementations, optical filter 400 may be disposed between aset of prisms. In another example, another incident medium may be used,such as a transparent epoxy, and/or another substrate may be used, suchas a polymer substrate (e.g., a polycarbonate substrate, a cyclic olefincopolymer (COP) substrate, or the like).

As indicated above, FIG. 4 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 4.

FIGS. 5A-5C are diagrams of another example of characteristics relatingto using an example implementation described herein.

As shown in FIG. 5A, and by chart 510, a set of optical characteristicsof a set of optical filters (e.g., a hydrogenated silicon (Si:H) basedoptical filter and a hydrogenated silicon-germanium (SiGe:H) basedoptical filter). In this case, the set of optical filters may utilizesilicon dioxide as a low index material. As shown, a transmissionpercentage at a set of wavelengths is determined for the set of opticalfilters. In this case, the SiGe:H optical filter is associated with arefractive index of 3.871 at 950 nm and the Si:H optical filter isassociated with a refractive index of 3.740 at 950 nm. As a result ofthe SiGe:H optical filter having a higher refractive index than the Si:Hoptical filter, the SiGe:H optical filter may be associated with areduced physical thickness. For example, the Si:H optical filter may beassociated with a 6.3 micrometer thickness and the SiGe:H optical filtermay be associated with a 5.4 micrometer thickness. Additionally, theSiGe:H optical filter may be associated with a greater blockingefficiency (e.g., the SiGe:H optical filter may be more absorbing atapproximately 700 nm than the Si:H optical filter resulting in a reducedquarter wave stack coating to block a wavelength range including 700nm).

As shown in FIG. 5B, chart 520 shows a portion of chart 510 at awavelength range of 950 nanometers to 1000 nanometers. As shown in chart520, the angleshift is shown to be 16.5 nm for the Si:H optical filterat an angle of incidence (AOI) from 0 degrees to 30 degrees and 13.0 nmfor the SiGe:H optical filter at an angle of incidence from 0 degrees to30 degrees. In this case, the SiGe:H optical filter is shown to have areduced angle shift relative to the Si:H optical filter resulting inimproved optical performance.

As shown in FIG. 5C, and by chart 530, a design of Si:H optical filtersand SiGe:H optical filters, such as the optical filters of FIGS. 5A and5B and a set of optical characteristics are shown. As shown the set ofoptical filters are associated with a substrate size of 200 mm to 300 mmand a substrate thickness of 0.15 mm to 0.7 mm. For each wafer size andwafer thickness, the SiGe:H optical filter is associated with a reducedsubstrate deflection relative to the Si:H optical filter. In this way,durability and manufacturability of an optical filter is improved.Moreover, based on reducing a stress value, a substrate size may beincreased for a similar substrate thickness relative to other substratedesigns, based on reducing a likelihood of braking during a singulationprocedure relative to other substrate designs with higher stress values.

As indicated above, FIGS. 5A-5C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 5A-5C.

FIGS. 6A and 6B are a diagrams of an example implementation 600described herein. As shown in FIG. 6A, example implementation 600includes a sensor system 610. Sensor system 610 may be a portion of anoptical system, and may provide an electrical output corresponding to asensor determination. Sensor system 610 includes an optical filterstructure 620, which includes an optical filter 630, and an opticalsensor 640. For example, optical filter structure 620 may include anoptical filter 630 that performs a passband filtering functionality oranother type of optical filter. Sensor system 610 includes an opticaltransmitter 650 that transmits an optical signal toward a target 660(e.g., a person, an object, etc.).

Although implementations, described herein, may be described in terms ofan optical filter in a sensor system, implementations described hereinmay be used in another type of system, may be used external to thesensor system, or the like. In some implementations, optical filter 630may perform a polarization beam splitting functionality for the light.For example, optical filter 630 may reflect a first portion of the lightwith a first polarization and may pass through a second portion of thelight with a second polarization when the second polarization is desiredto be received by the optical sensor 640, as described herein.Additionally, or alternatively, optical filter 630 may perform a reversepolarization beam splitting functionality (e.g., beam combining) for thelight.

As further shown in FIG. 6A, and by reference number 670, an inputoptical signal is directed toward optical filter structure 620. Theinput optical signal may include NIR light emitted by opticaltransmitter 650 and ambient light from the environment in which sensorsystem 610 is being utilized. For example, when optical filter 630 is abandpass filter, optical transmitter 650 may direct near infrared (NIR)light toward a user for a gesture recognition system (e.g., of a gestureperformed by target 660), and the NIR light may be reflected off target660 (e.g., a user) toward optical sensor 640 to permit optical sensor640 to perform a measurement of the NIR light. In this case, ambientlight may be directed toward optical sensor 640 from one or more ambientlight sources (e.g., a light bulb or the sun). In another example,multiple light beams may be directed toward target 660 and a subset ofthe multiple light beams may be reflected toward optical filterstructure 620, which may be disposed at a tilt angle relative to opticalsensor 640, as shown. In some implementations, another tilt angle may beused (e.g., a 0 degree tilt angle for a bandpass filter). In someimplementations, optical filter structure 620 may be disposed and/orformed directly onto optical sensor 640, rather than being disposed adistance from optical sensor 640. For example, optical filter structure620 may be coated and patterned onto optical sensor 640 using, forexample, photolithography. In another example, optical transmitter 650may direct NIR light toward another type of target 660, such as fordetecting objects in proximity to a vehicle, detecting objects inproximity to a blind person, detecting a proximity to an object (e.g.,using a LIDAR technique), or the like, and the NIR light and ambientlight may be directed toward optical sensor 640 as a result.

As further shown in FIG. 6A, and by reference number 680, a portion ofthe optical signal is passed by optical filter 630 and optical filterstructure 620. For example, alternating silicon-germanium layers (e.g.,a high index material) and another type of material layers (e.g., a lowindex material, such as silicon dioxide (SiO₂)) of optical filter 630may cause the first polarization of light to be reflected in a firstdirection. In another example, the high index material may includeanother silicon-germanium based material, such as hydrogenatedsilicon-germanium, annealed silicon-germanium, or the like as describedherein. In this case, optical filter 630 blocks visible light of theinput optical signal without excessively blocking NIR light and withoutintroducing an excessive angle-shift with an increase in an angle ofincidence of the input optical signal.

As further shown in FIG. 6A, and by reference number 690, based on theportion of the optical signal being passed to optical sensor 640,optical sensor 640 may provide an output electrical signal for sensorsystem 610, such as for use in recognizing a gesture of the user ordetecting the presence of an object. In some implementations, anotherarrangement of optical filter 630 and optical sensor 640 may beutilized. For example, rather than passing the second portion of theoptical signal collinearly with the input optical signal, optical filter630 may direct the second portion of the optical signal in anotherdirection toward a differently located optical sensor 640. In anotherexample, optical sensor 640 may be an avalanche photodiode, anIndium-Gallium-Arsenide (InGaAs) detector, an infrared detector, or thelike.

As shown in FIG. 6B, a similar example implementation 600 may includesensor system 610, optical filter structure 620, optical filter 630,optical sensor 640, optical transmitter 650, and target 660. FIG. 6Bshows a particular example implementation 600 that includes an opticalfilter 630 as described herein.

Optical transmitter 650 emits light at an emission wavelength in awavelength range of 800 nm to 1100 nm. Optical transmitter 650 emitsmodulated light (e.g., light pulses). Optical transmitter 650 may be alight-emitting diode (LED), an LED array, a laser diode, or a laserdiode array. Optical transmitter 650 emits light towards target 660,which reflects the emitted light back towards sensor system 610. Whensensor system 610 is a gesture-recognition system, target 660 is a userof the gesture-recognition system.

Optical filter 630 is disposed to receive the emitted light afterreflection by target 660. Optical filter 630 has a passband includingthe emission wavelength and at least partially overlapping with thewavelength range of 800 nm to 1100 nm. Optical filter 630 is a bandpassfilter, such as a narrow bandpass filter. Optical filter 630 transmitsthe emitted light from the optical transmitter 650, while substantiallyblocking ambient light.

Optical sensor 640 is disposed to receive the emitted light aftertransmission by optical filter 630. In some implementations, opticalfilter 630 is formed directly on optical sensor 640. For example,optical filter 630 may be coated and patterned (e.g., byphotolithography) on sensors (e.g., proximity sensors) in wafer levelprocessing (WLP).

When sensor system 610 is a proximity sensor system, optical sensor 640is a proximity sensor, which detects the emitted light to sense aproximity of target 660. When sensor system 610 is a 3D-imaging systemor a gesture-recognition system, optical sensor 640 is a 3D image sensor(e.g., a charge-coupled device (CCD) chip or a complementary metal oxidesemiconductor (CMOS) chip), which detects the emitted light to provide a3D image of target 660, which, for example, is the user. The 3D imagesensor converts the optical information into an electrical signal forprocessing by a processing system (e.g., an application-specificintegrated circuit (ASIC) chip or a digital signal processor (DSP)chip). For example, when sensor system 610 is a gesture-recognitionsystem, the processing system processes the 3D image of the user torecognize a gesture of the user.

As indicated above, FIGS. 6A and 6B are provided merely as an example.Other examples are possible and may differ from what was described withregard to FIGS. 6A and 6B.

In this way, a set of silicon-germanium based layers may be used as ahigh index material for an optical filter coating of an optical filterto provide out-of-band blocking of visible light, transmission of NIRlight, and/or filtering of light with a reduced angle shift relative toanother type of material used for a set of high index layers. Moreover,based on using hydrogenated silicon-germanium and/or an annealingprocedure, out-of-band blocking and in-band transmission are improvedrelative to another type of material.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise form disclosed. Modifications and variations are possible inlight of the above disclosure or may be acquired from practice of theimplementations.

Some implementations are described herein in connection with thresholds.As used herein, satisfying a threshold may refer to a value beinggreater than the threshold, more than the threshold, higher than thethreshold, greater than or equal to the threshold, less than thethreshold, fewer than the threshold, lower than the threshold, less thanor equal to the threshold, equal to the threshold, etc.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of possible implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of possible implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the term “set” is intended to include one or more items(e.g., related items, unrelated items, a combination of related items,and unrelated items, etc.), and may be used interchangeably with “one ormore.” Where only one item is intended, the term “one” or similarlanguage is used. Also, as used herein, the terms “has,” “have,”“having,” or the like are intended to be open-ended terms. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A sputter deposition system, comprising: a firstcathode; a second cathode; a first target, wherein the first target isoriented approximately parallel to a substrate, and wherein the firstcathode is configured to sputter a first material from the first target;and a second target, wherein the second target is oriented approximately120 degrees relative to the substrate, and wherein the second cathode isconfigured to sputter a second material from the second target.
 2. Thesputter deposition system of claim 1, wherein the first target is asilicon target.
 3. The sputter deposition system of claim 1, wherein thesecond target is a germanium target.
 4. The sputter deposition system ofclaim 1, wherein the first material is silicon.
 5. The sputterdeposition system of claim 1, wherein the second material is germanium.6. The sputter deposition system of claim 1, wherein the first target isa germanium target.
 7. The sputter deposition system of claim 1, whereinthe second target is a silicon target.
 8. The sputter deposition systemof claim 1, further comprising: a plasma activation source (PAS)configured to introduce hydrogen gas into a vacuum chamber that includesthe first cathode, the second cathode, the first target, and the secondtarget.
 9. A sputter deposition system, comprising: a first cathode; asecond cathode; a silicon target, wherein the first cathode isconfigured to sputter silicon from the silicon target onto a substrate;a germanium target; and wherein the second cathode is configured tosputter germanium from the germanium target onto the substrate.
 10. Thesputter deposition system of claim 9, wherein the silicon target isoriented at approximately 60 degrees relative to the substrate.
 11. Thesputter deposition system of claim 9, wherein the germanium target isoriented at approximately 60 degrees relative to the substrate.
 12. Thesputter deposition system of claim 9, further comprising: a plasmaactivation source (PAS) configured to introduce hydrogen gas into achamber that includes the first cathode and the second cathode.
 13. Thesputter deposition system of claim 12, wherein the chamber is a vacuumchamber.
 14. A sputter deposition system, comprising: a substrate; and atarget that includes silicon-germanium material, wherein the target isconfigured to be sputtered in presence of hydrogen to deposit ahydrogenated silicon-germanium material as a layer on the substrate. 15.The sputter deposition system of claim 14, wherein the target isconfigured to be sputtered in presence of the hydrogen and an inert gas.16. The sputter deposition system of claim 15, wherein the inert gas isargon.
 17. The sputter deposition system of claim 14, furthercomprising: a cathode, wherein an angle of the cathode causes aparticular concentration of silicon-germanium to be sputtered onto thesubstrate.
 18. The sputter deposition system of claim 14, furthercomprising: a plasma activation source (PAS) configured to introduce thehydrogen.
 19. The sputter deposition system of claim 14, wherein thesubstrate and the target are in a vacuum chamber.
 20. The sputterdeposition system of claim 14, wherein the hydrogenatedsilicon-germanium material is deposited at a deposition rate ofapproximately 0.05 nanometers (nm)/second(s) to approximately 2.0 nm/s.